The present disclosure relates to viewers having varifocal lenses and automatically adjusting focal lengths of the lenses in accordance with eye movement of users.
Human beings move their gazing points, i.e., points of fixation, by means of eye movement. The eyes also move when the gazing points move in the depth direction. This movement is particularly called vergence eye movement.
Japanese Unexamined Patent Publication No. H04-273211 describes a technique in which a gazing point is obtained by detecting a change in electro-oculogram caused by eye movement so that the focal length of a varifocal lens is adjusted in accordance with the gazing point.